The present invention relates to substrate-guided optical devices, and particularly to devices which include a plurality of reflecting surfaces carried by a common light-transmissive substrate.
The invention can be implemented in a large number of applications, such as, for example, head-mounted and head-up displays, compact displays, compact beam expanders and flat-panel illuminators.
One of the important applications for compact optical elements is in head-mounted displays wherein an optical module serves both as an imaging lens and a combiner, in which a two-dimensional display is imaged to infinity and reflected into the eye of an observer. The display can be obtained directly, from either a cathode ray tube (CRT) or a liquid crystal display (LCD), or indirectly, by means of a relay lens or an optical fiber bundle. Typically, the display is comprised of an array of points which is imaged to infinity by a collimating lens and transmitted into the eye of the viewer by means of a partially reflecting surface acting as a combiner. Usually, a conventional, free-space optical module is used for these purposes. Unfortunately, however, as the desired field-of-view (FOV) of the system is increased, the optical module becomes heavier, bulky and very complicated to use. This is a major drawback in head-mounted applications, wherein the system should be as light and as compact as possible.
Other drawbacks of the existing designs are that with these designs, the overall optical systems are usually very complicated and difficult to manufacture. Furthermore, the eye-motion-box of the optical viewing angles resulting from these designs is usually very smallxe2x80x94typically less than 8 mm. Hence, the performance of the optical system is very sensitive, even to small movements of the visor relative to the eye of the viewer.
The present invention may be used for designing and fabricating substrate-guided optical elements for visor displays in which the optical module is very compact and easy to use, even for systems with relatively high FOVs. In addition, the eye-motion-box of the optical system is relatively large and can therefore accommodate large movements of the visor. The system of the invention is particularly advantageous because it is very compact and can be readily incorporated, even into optical systems having specialized configurations.
The invention also enables the construction of improved head-up displays (HUDs). Since the inception of such displays more than three decades ago, there has been significant progress in the field. Indeed, HUDs have become so popular that they now play an important role, not only in all modern combat aircraft, but also in civilian aircraft, in which HUD systems play an important role during the landing operation. Furthermore, there have recently been numerous proposals and designs for the installation of HUDs in automobiles to assist in driving and navigation duties.
Yet the current form of HUDs has some severe drawbacks. The necessity to use a display source that must be located at some distance from the combiner so as to illuminate its whole surface, makes the HUDs bulky, large, and sometimes inconvenient and unsafe to use.
Another important application of the present invention is in providing a compact HUD which overcomes the above drawbacks. The combiner can be illuminated with a compact display source that is attached to the substrate. Hence, the overall system is very compact and can thus be installed easily and used in a variety of places and applications. In addition, the chromatic dispersion of the display is relatively small and, as such, the light source can have a wide spectrum, even like that of a conventional white-light source. In addition, the area of the display can be much larger than the area that is actually illuminated by the light source.
A further application of the present invention is to provide a compact beam expander. Beam expanders for magnifying a narrow collimated beam into a beam with a larger diameter, typically comprise a telescopic assembly of two lenses along a common axis, with a common focal point. The present invention provides a beam expander that can be used with both monochromatic and polychromatic light.
The broad object of the present invention, therefore, is to ameliorate the drawbacks of the known devices and to provide optical systems having improved performance, according to specific requirements.
The invention therefore provides an optical device comprising a light-transmitting planar substrate; optical means for coupling light into said substrate by total internal reflection, and a plurality of partially reflecting surfaces carried by said substrate, characterized in that said partially reflecting surfaces are parallel to each other and are not parallel or normal to the plane of said substrate.